title: Decreased inhibitory neuronal activity in patients with frontal  lobe brain tumors with seizure presentation: Preliminary  study using magnetoencephalography.
abstract: BACKGROUND
  Although 30-50 % of patients with brain tumors experience epileptic seizure as the presenting clinical symptom, and another 10-30 % are at risk for developing epilepsy in the later stages of the disease, the mechanisms of tumor-related epileptogenesis are poorly understood. We used magnetoencephalography (MEG) to investigate sensory evoked fields (SEFs) in patients with frontal lobe brain tumors as a means of evaluating the neuronal activity of peri-tumoral cortex.
  
  
  METHODS
  Twelve patients with frontal lobe brain tumors underwent MEG. We calculated the equivalent current dipole strength of two components of the primary sensory cortical response (N20m and P35m) and compared the P35m/N20m ratio in the tumor hemisphere vs. the normal hemisphere. There were two subsets of patients: group I, in which P35m/N20m was higher in the tumor hemisphere (n= 7), and group II, in which P35m/N20m was higher in the normal hemisphere (n=5). We looked for associations between clinical factors and P35m/N20m within each group.
  
  
  RESULTS
  All patients with seizure presentation were in group I, whereas only two patients without seizure presentation were in group I (Fisher exact test, p=0.028). No other clinical factors were related to P35m/N20m. The mean ratio of P35m/N20m equivalent current dipole strength in patients with seizure presentation was 4.07 ± 2.38 in the tumor hemisphere and 2.00 ± 0.55 in the normal hemisphere. This difference was statistically significant (Mann-Whitney test, p=0.030).
  
  
  CONCLUSIONS
  The paradoxical increase in P35m/N20m in patients with seizure presentation suggests that decreased inhibitory neuronal activity is a potential cause of tumorrelated epilepsy.
authors.affiliation: Department of Neurosurgery, Brain Research Institute, Yonsei University College of Medicine, 205 Seongsanno Seodaemun-gu, Seoul 120-752, Korea.
authors.forename: Won Seok
authors.initials: WS
authors.lastname: Chang
authors.forename: Bong Soo
authors.initials: BS
authors.lastname: Kim
authors.forename: Hyun Ho
authors.initials: HH
authors.lastname: Jung
authors.forename: Kiwoong
authors.initials: K
authors.lastname: Kim
authors.forename: Hyuk Chan
authors.initials: HC
authors.lastname: Kwon
authors.forename: Yong Ho
authors.initials: YH
authors.lastname: Lee
authors.forename: Jin Woo
authors.initials: JW
authors.lastname: Chang
mesh_terms: D000328:Adult; D000368:Aged; D001932:Brain Neoplasms / Q000150:complications / Q000473:pathology / Q000503:physiopathology*; D004558:Electric Stimulation / Q000379:methods; D005073:Evoked Potentials, Somatosensory / Q000502:physiology*; D005260:Female; D005625:Frontal Lobe / Q000503:physiopathology*; D006801:Humans; D015225:Magnetoencephalography; D008297:Male; D008475:Median Nerve / Q000503:physiopathology; D008875:Middle Aged; D012640:Seizures / Q000209:etiology / Q000473:pathology / Q000503:physiopathology* / Q000628:therapy; D013003:Somatosensory Cortex / Q000473:pathology / Q000502:physiology / Q000503:physiopathology*; D055815:Young Adult